7-(1,3-Dithiolan-2-imino)-Δ2 -cephalosporanic acid derivatives

ABSTRACT

Novel 7-(1,3-dithiolan-2-imino)-Δ 2  -cephalosporanic acid derivatives are described which possess useful antibacterial properties.

This is a division of application Ser. No. 19,415, filed Mar. 12, 1979,now U.S. Pat. No. 4,208,516.

TECHNICAL FIELD

This invention relates to certain cephalosporin derivatives useful asantibacterial agents and to a method for their preparation.

BACKGROUND ART

Compounds with a cephalosporin nucleus belong to a well-known family ofantibiotics that have been widely used in recent years for the treatmentof various infectious diseases. A number of commercially usefulcephalosporin antibiotics have been obtained by varying the substitutionat the 3-position of the cephalosporin nucleus and by variousmodifications of the side-chain substituents at the 7-position of thecephalosporin nucleus. The search continues, however, for new compoundswhich possess a broad spectrum of antibacterial activity and whichpossess a high degree of activity toward both gram-positive andgram-negative bacteria without causing undesirable contraindicationswhen administered to humans.

In an effort to improve upon the antibacterial properties of existingcompounds, efforts have been directed towards the introduction of a1,3-dithiolan ring directly at the 7-position of the cephalosporinnucleus. More particularly, the preparation of such cephalosporanic acidderivatives having in addition an acyl or alkyl derivative in the4-position and a shift of unsaturation to the Δ² -position of thecephalosporin nucleus provides a novel class of cephalosporinderivatives that are effective against one or more gram-positive andgram-negative microorganisms. Accordingly, the compounds of the presentinvention are effective in the treatment of various infectious diseasescaused by such gram-positive and gram-negative bacteria in poultry or inmammals including man. The compounds herein disclosed are suitable foruse in certain topical germicidal preparations or as surfacedisinfectants.

SUMMARY OF THE INVENTION

In accordance with this invention certain novel7-(1,3-dithiolan-2-imino)-Δ² -cephalosporanic derivatives are described,that are useful for their antibacterial properties. More particularly,this invention relates to certain 4-alkylated or 4-acylated derivativesof 7-(1,3-dithiolan-2-imino)-Δ² -cephalosporanic acids having theformula: ##STR1## wherein R₁ is selected from the group consisting ofhydrogen, acetoxy, 5-methyl-1,3,4-thiadiazol-2-ylthio,1-methyl-1,2,3,4-tetrazol-5-ylthio and 1,2,3-triazol-4-ylthio; R₂ isselected from the group consisting of hydrogen, t-butyl,2,2,2-trichloroethyl, benzhydryl, formyloxymethyl and alkanoyloxymethylin which the alkanoyl group contains from 2 to 5 carbon atoms; R₃ isselected from the group consisting of alkyl having from 1 to 4 carbonatoms, carboxymethyl, alkoxycarbonyl and (alkoxycarbonyl)methyl whereinthe alkoxy group has from 1 to 4 carbon atoms, halomethyl, benzyl andsubstituted benzyl wherein the benzyl substituent is methoxy or halo;and the pharmaceutically acceptable salts thereof.

Another aspect of this invention relates to the preparation of thesenovel 7-(1,3-dithiolan-2-imino)-Δ² -cephalosporanic acid derivatives byreacting a 7-(1,3-dithiolan-2-imino)cephalosporanic acid having theformula ##STR2## with an alkylating or acylating agent having theformula R₃ Y, wherein the symbols R₁, R₂ and R₃ are as previouslydefined and Y is a leaving group selected from the group consisting ofhalogen, alkoxy, alkylthio, alkoxycarbonylthio, --OSO₂ Z and ##STR3##wherein Z is alkyl, alkoxy and tolyl and each of the alkyl or alkoxygroups have from 1 to 4 carbon atoms; reacting said cephalosporanic acidand alkylating or acylating agent in an anhydrous organic solvent at atemperature of from -78° C. to 30° C. for a period of from 1 to 24 hoursin the presence of a strong base; and recovering the7-(1,3-dithiolan-2-imino)-Δ² -cephalosporanic acid therefrom.

This process is particularly useful in that it provides a convenientmethod for the direct insertion of various alkyl, substituted alkyl orsubstituted acyl groups directly at the 4-position of the cephalosporinnucleus.

DETAILED DESCRIPTION OF THE INVENTION

As can be seen in formula (1) above, all of the compounds of thisinvention contain a 1,3-dithiolan-2-imino moiety attached directly tothe 7-position of Δ² -cephalosporin nucleus. In addition, all of thecompounds contain an alkyl, substituted alkyl or substituted acyl groupat the 4-position of a Δ² -cephalosporin nucleus.

The term cephalosporanic acid derivatives as used herein relates ingeneral to the specific cephalosporanic acids defined by the varioussubstituents on the 3-methyl group of the cephalosporin nucleus. Thus,where the symbol R₁ is hydrogen, the compounds are designated asdesacetoxycephalosporanic acids. When the symbol R₁ represents theacetoxy group, the compounds are specifically designated as belonging tothe class of cephalosporanic acids. Finally, the symbol R₁ can representa heterocyclic thioether attached to the 3-methyl group of thecephalosporin nucleus. The preferred heterocyclic thio-ethers describedherein include the 5-methyl-1,3,4-thiadiazol-2-ylthio group, the1-methyl-1,2,3,4-tetrazol-5-ylthio group and the 1,2,3-triazol-4-ylthiogroup. In order to be consistent with the nomenclature employed herein,these heterocyclic thioethers are designated as3-[(heterocycle-ylthio)methyl]decephalosporanic acids.

The compounds contemplated within the scope of this invention includenot only the free cephalosporanic acids, but certain esters thereof asfurther indicated by the symbol R₂. Thus, where the symbol R₂ representshydrogen, the free acid is designated. The preferred cephalosporanicacid ester groups include the t-butyl, 2,2,2-trichloroethyl, benzhydryl,formyloxymethyl and alkanoyloxymethyl groups. The term alkanoyl as usedin this regard includes those groups having a total of from 2 to 5carbon atoms, as for example, the acetyl, propionyl, butyryl,isobutyryl, 2-methylbutyryl, 3-methylbutyryl and 2,2-dimethylpropionylgroups. In general, these ester groups confer improved absorptionproperties upon the molecule, while remaining physiologically labile.Such esters are readily absorbed from the gastrointestinal tract,thereby promoting oral activity, whereupon they are enzymaticallyhydrolyzed to the corresponding free, and generally more active,cephalosporanic acids. These esters are readily prepared in accordancewith the procedures described by Binderup et al., Journal ofAntibiotics, 24, 767 (1971).

All of the compounds of this invention contain an alkyl, substitutedalkyl or substituted acyl group at the 4-position of the cephalosporinnucleus as defined by the symbol R₃. When R₃ represents an alkyl group,a preferred sub-generic group of compounds is delineated. As employedherein, the term alkyl or alkoxy is intended to refer to those straightor branched chain groups having from 1 to 4 carbon atoms, e.g., methyl,methoxy, ethyl, ethoxy, propyl, propoxy, butyl, butoxy, isopropyl,isopropoxy, isobutyl, isobutoxy, sec. butyl and sec. butoxy.

The remaining alkyl groups defined by the symbol R₃ can be regarded asbeing substituted methyl derivatives. Thus, the symbol R₃ alsorepresents a carboxy substituted methyl group, termed herein as thecarboxymethyl group; a formic acid ester substituted methyl group,termed herein as an alkoxycarbonylmethyl group; a halogen substitutedmethyl group, designated herein as an halomethyl group; and a phenyl or(substituted)phenyl methyl group, designated herein as a benzyl orsubstituted benzyl group. The phenyl portion of the benzyl group mayremain unsubstituted or can be mono-substituted in either of the ortho,meta or para positions of the phenyl ring with a halogen or a methoxygroup. As used herein and throughout the specification, the term halogenis intended to particularly include the fluorine, chlorine and brominemembers of the halogen family.

The symbol R₃ also includes certain acyl groups substituted at the4-position of the cephalosporin nucleus. More particularly, variouslower alkyl esters of formic acid are contemplated to be within thescope of this invention and are collectively designated as analkoxycarbonyl group, wherein the term alkoxy is as previously defined.

The pharmaceutically acceptable salts of the compounds of formula (1)include the non-toxic, carboxylic acid salts that are formed with anysuitable inorganic or organic base. Illustratively, these salts includethose of alkali metals, as for example, sodium and potassium; alkalineearth metals, such as barium, calcium and magnesium; light metals ofGroup III A including aluminum; and organic primary, secondary andtertiary amines including triethylamine, procaine, dibenzylamine,vinylamine, N,N'-dibenzylethylenediamine, dihydroabietylamine,N-(lower)alkylpiperidine and various other amines that have been used toform non-toxic salts of antibiotics such as benzylpenicillin. Thesesalts are prepared via conventional methods known to those skilled inthe art, as for example by the neutralization of a solution of the freecarboxylic acid in a polar solvent using a stoichiometric quantity ofbase, and recovering the salt therefrom.

Illustrative compounds encompassed by formula (1) above include:

7-(1,3-dithiolan-2-imino)-4-ethyl-Δ² -cephalosporanic acid,

7-(1,3-dithiolan-2-imino)-4-carboxymethyl-Δ² -cephalosporanic acid,

t-butyl 7-(1,3-dithiolan-2-imino)-4-ethoxycarbonyl-Δ² -cephalosporanate,

2,2,2-trichloroethyl 7-(1,3-dithiolan-2-imino)-4-butoxycarbonyl-Δ²-cephalosporanate,

benzhydryl 7-(1,3-dithiolan-2-imino)-4-methoxycarbonylmethyl-Δ²-cephalosporanate,

formyloxymethyl 7-(1,3-dithiolan-2-imino)-4-chloromethyl-Δ²-cephalosporanate,

pivaloyloxymethyl 7-(1,3-dithiolan-2-imino)-4-benzyl-Δ²-cephalosporanate,

7-(1,3-dithiolan-2-imino)-4-isopropyl-Δ² -desacetoxycephalosporanicacid,

7-(1,3-dithiolan-2-imino)-4-methoxycarbonyl-Δ²-desacetoxycephalosporanic acid,

formyloxymethyl 7-(1,3-dithiolan-2-imino) -4-butyl-Δ²-desacetoxycephalosporanate,

pivaloyloxymethyl 7-(1,3-dithiolan-2-imino)-4-carboxymethyl-Δ²-desacetoxycephalosporanate,

benzhydryl 7-(1,3-dithiolan-2-imino)-4-bromomethyl-Δ²-desacetoxycephalosporanate,

t-butyl 7-(1,3-dithiolan-2-imino)-4-p-methoxybenzyl-Δ²-desacetoxycephalosporanate,

7-(1,3-dithiolan-2-imino)-4-butyl-3-[(5-methyl-1,3,4-thiadiazol-2-ylthio)methyl]-Δ²-decephalosporanic acid,

7-(1,3-dithiolan-2-imino)-4-carboxymethyl-3-[(5-methyl-1,3,4-thiadiazol-2-ylthio)methyl]-Δ²-decephalosporanic acid,

t-butyl7-(1,3-dithiolan-2-imino)-4-butoxycarbonyl)-3-[(5-methyl-1,3,4-thiadiazol-2-ylthio)methyl]-Δ²-decephalosporanate,

benzhydryl7-(1,3-dithiolan-2-imino)-4-ethoxycarbonylmethyl-3-[(5-methyl-1,3,4-thiadiazol-2-ylthio)methyl]-Δ²-decephalosporanate,

acetyloxymethyl7-(1,3-dithiolan-2-imino)-4-benzyl-3-[(5-methyl-1,3,4-thiadiazol-2-ylthio)methyl]-Δ²-decephalosporanate,

2-methylbutyryloxymethyl7-(1,3-dithiolan-2-imino)-4-o-bromobenzyl-3-[(5-methyl-1,3,4-thiadiazol-2-ylthio)methyl]-Δ²-decephalosporanate,

7-(1,3-dithiolan-2-imino)-4-methyl-3-[(1-methyl-1,2,3,4-tetrazol-5-ylthio)methyl]-Δ²-decephalosporanic acid,

7-(1,3-dithiolan-2-imino)-4-propoxycarbonyl-3-[(1-methyl-1,2,3,4-tetrazol-5-ylthio)methyl]-Δ²-decephalosporanic acid,

t-butyl7-(1,3-dithiolan-2-imino)-4-butoxycarbonylmethyl-3-[(1-methyl-1,2,3,4-tetrazol-5-ylthio)methyl]-Δ²-decephalosporanate,

2,2,2-trichloroethyl7-(1,3-dithiolan-2-imino)-4-chloromethyl-3-[(1-methyl-1,2,3,4-tetrazol-5-ylthio)methyl]-Δ²-decephalosporanate,

formyloxymethyl7-(1,3-dithiolan-2-imino)-4-benzyl-3-[(1-methyl-1,2,3,4-tetrazol-5-ylthio)methyl]-Δ²-decephalosporanate,

pivaloyloxymethyl7-(1,3-dithiolan-2-imino)-4-m-methoxybenzyl-3-[(1-methyl-1,2,3,4-tetrazol-5-ylthio)methyl]-Δ²-decephalosporanate,

7-(1,3-dithiolan-2-imino)-4-carboxymethyl-3-[(1,2,3-triazol-4-ylthio)methyl]-Δ²-decephalosporanic acid,

7-(1,3-dithiolan-2-imino)-4-benzyl-3-[(1,2,3-triazol-4-ylthio)methyl]-.DELTA.²-decephalosporanic acid,

pivaloyloxymethyl7-(1,3-dithiolan-2-imino)-4-chloromethyl-3-[(1,2,3-triazol-4-ylthio)methyl]-Δ²-decaphalosporanate.

formyloxymethyl7-(1,3-dithiolan-2-imino)-4-ethoxycarbonyl-3-[(1,2,3-triazol-4-ylthio)methyl]-Δ²-decephalosporanate,

2,2,2-trichloroethyl7-(1,3-dithiolan-2-imino)-p-chlorobenzyl-3-[(1,2,3-triazol-4-ylthio)methyl]-Δ²-decephalosporanate, and

t-butyl7-(1,3-dithiolan-2-imino)-o-methoxybenzyl-3-[(1,2,3-triazol-4-ylthio)methyl]-Δ²-decephalosporanate.

The 7-(1,3-dithiolan-2-imino)-Δ² -cephalosporanic acid derivatives ofthis invention are readily prepared by reacting a7-(1,3-dithiolan-2-imino)cephalosporanic acid with an alkylating oracylating agent as indicated below. ##STR4##

In the above reaction scheme the symbols R₁, R₂ and R₃ are as previouslydefined and the symbol Y represents a typical "leaving group". Thus, inthe case where R₃ represents an alkyl or substituted alkyl group, thesymbol Y can represent an anion such as halogen, alkoxy, alkylthio,alkoxycarbonylthio or --OSO₂ Z, wherein the terms alkyl and alkoxy areas previously defined and Z is an alkyl, alkoxy or tolyl group. Where R₃represents a carboxy or substituted acyl group, the symbol Y representsan anion such as ##STR5##

The reaction is conducted in the presence of a strong base, preferablyan organometallic base of one of the alkali metals. These bases includethe alkali lower alkoxides such as potassium t-butoxide, sodiummethoxide, lithium methoxide, triphenylmethyl lithium, lithiumalkylamides such as lithium diisopropylamide or lithium cyclohexylisopropylamide, and alkali metal hydrides such as sodium and potassiumhydride. Approximately one equivalent (or a slight excess thereof) isrequired for the strong base, calculated on the basis of the startingmaterial. Preferably, the strong base of choice is a freshly preparedsolution of lithium diisopropylamide.

The starting material, alkylating or acylating agent and the strong baseare caused to react in an inert, anhydrous organic solvent which doesnot interfere with the reaction. Various inert solvents which can beemployed include dimethoxyethane, dioxane, tetrahydrofuran,dimethylformamide, dimethylsulfoxide, benzene, ether and other relatedreaction media. The solvents most preferably employed includedimethylformamide or tetrahydrofuran and/or mixtures thereof.

The reaction is conducted at a temperature ranging from -78° C. to 30°C. for a period of from 1 to 24 hours. Preferably the reaction isinitially conducted at -50° C. and gradually permitted to warm to roomtemperature with continued stirring. The reaction mixture is quenched bydilution and the desired product isolated using techniques well known tothose skilled in the art. Thus, for example, the quenched reactionmixture is extracted with an organic solvent such as chloroform,methylene chloride or ether, the combined organic extracts are dried andevaporated in vacuo, and the residue is purified by crystallization froma suitable organic solvent or organic solvent mixture.

Depending upon the particular 7-(1,3-dithiolan-2-imino)cephalosporanicstarting materials and reaction conditions employed, alkylation at the4-position of the cephalosporin nucleus can result in the formation ofboth cis and trans isomers of the β-lactam nucleus. Thus, treatment ofbenzhydryl 7-(1,3-dithiolan-2-imino)desacetoxycephalosporanate orbenzhydryl 7-(1,3-dithiolan-2-imino)cephalosporanate with lithiumdiisopropylamide in tetrahydrofuran at -50° C., followed by addition ofan alkylating agent such as methyl iodide and permitting the reactionmixture to warm to 20° C., affords good yields of benzhydryl7-(1,3-dithiolan-2-imino)-4-methyl-Δ² -desacetoxycephalosporanate and7-(1,3-dithiolan-2-imino)-4-methyl-Δ² -cephalosporanate, respectively,both with cis β-lactams. Treatment of t-butyl7-(1,3-dithiolan-2-imino)desacetoxycephalosporanate under identicalconditions affords a 1:1 mixture of the corresponding cis and transβ-lactam isomers.

On the other hand, treating benzhydryl7-(1,3-dithiolan-2-imino)desacetoxycephalosporanate, benzhydryl7-(1,3-dithiolan-2-imino)cephalosporanate, or t-butyl7-(1,3-dithiolan-2-imino)desacetoxycephalosporanate with lithiumdiisopropylamide at -50° C., permitting the reaction mixture to warm to20° C. and then adding the alkylating agent at this elevatedtemperature, results in the formation of the corresponding 4-alkylatedcompounds having only the trans β-lactam configuration. Moreover,treatment of the 4-alkylated compounds having the cis β-lactamconfiguration with lithium diisopropylamide at temperatures above 20° C.can result in an epimerization at the 7-position to yield compoundshaving the trans β-lactam configuration. Thus, for example, athermodynamic ratio of the trans:cis β-lactam isomers is achieved withbenzhydryl 7-(1,3-dithiolan-2-imino)-4-methyl-Δ²-desacetoxycephalosporanate by treating this compound with triethylaminein dimethylsulfoxide at room temperature to 45° C. for approximately 90hours.

The 7-(1,3-dithiolan-2-imino)cephalosporanic acids (II) used as startingmaterials are conveniently prepared and in good yield by condensing anS-alkylated salt of 1,3-dithiolane-2-thione (III) with a7-aminocephalosporanic acid. This reaction sequence is indicated asfollows wherein the symbols R₁ and R₂ are as previously defined and thesymbol X represents a halogen atom selected from the group consisting ofchlorine, bromine and iodine. ##STR6##

The S-alkylated salts of 1,3-dithiolane-2-thione are readily prepared bythe alkylation of 1,3-dithiolane-2-thione, which is known commerciallyas ethylenetrithiocarbonate. Thus, for example, the addition of a methylhalide with stirring to a solution of 1,3-dithiolane-2-thione at atemperature ranging from 0° to about 50° C. for a period of from 1 to 24hours results in the formation of the corresponding S-methyl halide saltof 1,3-dithiolene-2-thione as a crystalline salt. The S-methyl iodidesalt of 1,3-dithiolane-2-thione is the alkylated salt of choice and isprepared by the addition of methyl iodide to a solution of1,3-dithiolane-2-thione. Preferably, the reaction is conducted via thedropwise addition of methyl iodide to a nitromethane solution of1,3-dithiolane-2-thione at room temperature under an inert atmospheresuch as nitrogen or argon.

The various 7-aminocephalosporanic acids employed herein (V) arewell-known compounds previously described in the literature. Thus,hydrolysis of cephalosporin C results in the formation of7-aminocephalosporanic acid as described by Loder et al., Biochem. J.79, 408-16 (1961) and represented by the formula ##STR7##

The compound 7-aminodesacetoxycephalosporanic acid, having the formula##STR8## is prepared by the catalytic reduction of cephalosporin C,followed by the hydrolytic removal of the 5-aminoadipoyl side chain asdescribed in U.S. Pat. No. 3,129,224.

The 7-aminocephalosporanic acid derivatives (V) are readily condensed astheir free acids to form the 7-(1,3-dithiolan-2-imino)cephalosporanicacid derivatives (II) used as starting materials. Preferably, however,they are condensed in the form of their salts or their esters. Suitablesalts include the sodium and trialkylamine salts, in which the alkylgroup contains from 1 to 5 carbon atoms. Suitable esters include any ofthe esters disclosed in U.S. Pat. No. 3,284,451, or any of the silylesters analogously disclosed in U.S. Pat. No. 3,249,622. The condensedesters are readily isolated or, as in the case of the silyl esters, theyare readily cleaved to yield the free acids of the various7-(1,3-dithiolan-2-imino) cephalosporanic acid derivatives.

In general, the condensation of the 7-aminocephalosporanic acidderivatives (V) and the S-alkylated salts of 1,3-dithiolan-2-thione (IV)is conducted in the presence of a suitable solvent at temperaturesranging from -30° C. to 100° C. The reaction time varies from 15 minutesto as long as 36 hours depending upon the particular reactiontemperature employed. For convenience, the reaction is preferablyconducted at room temperature or slightly below for a period of from 1to 8 hours.

Suitable solvents in which the condensation takes place include acetone,acetonitrile, dioxane, dimethylformamide, chloroform, ethylene chloride,dichloromethane and tetrahydrofuran with acetonitrile being theparticular solvent of choice. In certain instances, as when the7-aminocephalosporanic acid starting materials are present in the formof a salt, mixtures of water and a miscible organic solvent may beadvantageously employed. Optionally, the condensation can be conductedin the presence of an inert atmosphere, as for example argon or nitrogengas. An excess of the S-alkylated salt of 1,3-dithiolane-2-thione (IV)is also favorably employed to insure completeness of the reaction and tofavor the yield of desired product obtained.

Following completion of the condensation reaction, the reaction mixtureis generally quenched in water and the desired7-(1,3-dithiolan-2-imino)cephalosporanic acid derivatives isolated viastandard procedures known to those versed in the art. Thus, for example,the quenched reaction mixture is extracted with a suitable organicsolvent, such as chloroform, methylene chloride or ether, the organicextract is washed with a dilute aqueous acid solution to remove anyunreacted starting material, the washed organic extract is dried,concentrated and the desired 7-(1,3-dithiolan-2-imino)cephalosporanicacid derivatives recovered therefrom. Purification of the products isgenerally effected by recrystallization from suitable organic solventssuch as chloroform from a chloroform-ether mixture.

When the 7-aminocephalosporanic acid derivatives (V) are present as thefree acid, i.e., where the symbol R₂ is hydrogen, the use of asilylating agent is advantageously employed. Under these circumstancesthe condensation best proceeds under anhydrous conditions in anhydroussolvents in which the free acids are not too soluble. The silylatingagents employed form labile silyl esters with the various7-aminocephalosporanic acids and are readily soluble in anhydroussolvents. Inasmuch as these silyl esters are highly sensitive tomoisture, once condensation has taken place, the esters are readilyhydrolyzed to the free acid by quenching the reaction mixture in water.Suitable silylating agents that may be favorably employed includevarious alkyl chlorosilanes, alkyl disilazanes, alkyl silylamines andalkylsilylamides, as for example triethyl chlorosilane, tri-n-butylchlorosilazane, dimethylethyl chlorosilane, phenylethylmethylchlorosilane, triphenyl chlorosilane, tetraethyldimethyl disilazane,hexamethyl disilazane, tetramethyldiphenyl disilazane, hexaphenyldisilazane, N-ethyl triethyl silylamine, triphenyl silylamine,N-trimethylsilylacetamide with the silylating agent of choice beingO,N-bis-trimethylsilylacetamide.

In general, the free acids of the 7-aminocephalosporanic acidderivatives (V), are suspended in a suitable anhydrous solvent, as forexample acetonitrile, tetrahydrofuran or dioxane. Two equivalents of thesilylating agent are added to this suspension and stirring is continueduntil esterification and solution occur, generally in about two hours orless at room temperature. An additional 10% excess of the silylatingagent is added to insure complete esterification of the particular7-aminocephalosporanic acid employed. Condensation with an S-alkylatedsalt of 1,3-dithiolane-2-thione and the subsequent isolation of thedesired products remain essentially as previously described.

A preferred group of 7-(1,3-dithiolan-2-imino)-4-substituted-Δ²-cephalosporanic acid derivatives (I) are those containing amethylthioheterocycle group at the 3-position of the cephalosporinnucleus. In addition to the condensation procedure described above,these compounds can be prepared by a displacement of the 3-acetoxy groupof a salt or ester of a 7-(1,3-dithiolan-2-imino)-4-substituted-Δ²-cephalosporanic acid. This displacement or solvolysis of the acetoxygroup at the 3-methyl position of the cephalosporin nucleus is awell-known reaction described in U.S. Pat. Nos. 3,516,997 and 3,641,021.The acetoxy group is readily displaced with a heterocyclic thiol, suchas 5-methyl-1,3,4-thiadiazol-2-ylthio,1-methyl-1,2,3,4-tetrazol-5-ylthio or 1,2,3-triazol-4-thiol attemperatures ranging from about 25° C. to 150° C. in aqueous solventssuch as water or buffered aqueous solutions. Preferably, a temperaturerange of from 50° C. to 100° C. is employed in combination with abuffered aqueous solution having a pH ranging from 4.0 to 9.0. Suitableaqueous solutions include those selected from the group consisting ofwater, or an aqueous solution of acetone, tetrahydrofuran anddimethylformamide.

The novel compounds of the present invention are useful antimicrobialagents having a broad spectrum of antimicrobial activity in vitroagainst standard laboratory microorganisms that are routinely used todemonstrate activity against pathogenic bacteria. The antibacterialspectrum of typical compounds described herein is determined in astandard manner by means of a qualitative diffusion assay as illustratedin Example 7 below. The in vitro antibacterial activity of the novelcompounds of this invention not only makes them useful aspharmacological agents per se, but makes them useful as additives foranimal feeds, as well as additives for materials which are subject tomicrobial deterioriation, such as cutting oils and fuel oils. Thesecompounds are also useful for their antibacterial effect in soaps,shampoos and in topical compositions for the treatment of wounds andburns.

The invention described herein is more particularly illustrated inconjunction with the following specific examples.

EXAMPLE 1 Benzhydryl 7-(1,3-dithiolan-2-imino)-4-methyl-Δ²-cephalosporanate

Butyl lithium, 0.46 ml, is added with stirring to 0.16 ml ofdiisopropylamine dissolved in 10 ml of dry tetrahydrofuran (freshlydistilled from lithium aluminum anhydride) at -50° C. under an argonblanket. A solution of 0.54 g of benzhydryl7-(1,3-dithiolan-2-imino)cephalosporanate dissolved in 10 ml ofdimethylformamide is added with stirring to the prepared lithiumdiisopropylamide solution at -50° C. To the red-colored solution thatforms is added 0.8 ml of methyl iodide. The reaction mixture is stirredat -50° C. for 10 minutes and allowed to warm to room temperature withcontinued stirring for an additional 20 minutes. The reaction mixture isquenched in pH 4.5 phosphate buffer, and the entire mixture extractedwith chloroform. The chloroform extracts are combined, washed withwater, dried (magnesium sulfate) and evaporated in vacuo to provide 0.68g of a light yellow oil. This residue is purified by dissolving in anether/ethyl acetate mixture and extracting the solution three times withwater and once with a saturated solution of sodium chloride. The organiclayer is dried over anhydrous magnesium sulfate and the solvents areremoved by evaporation in vacuo. The benzhydryl7-(1,3-dithiolan-2-imino)-4-methyl-Δ² -cephalosporanate so obtained hasthe appearance of a solid light yellow dried foam and has a m.pt. of55°-63° C. (dec.).

Following essentially the same procedure, but substituting t-butyl7-(1,3-dithiolan-2-imino)cephalosporanate, 2,2,2-trichloroethyl7-(1,3-dithiolan-2-imino)cephalosporanate, formyloxymethyl7-(1,3-dithiolan-2-imino)cephalosporanate and pivaloyloxymethyl 7-(1,3-dithiolan-2-imino)cephalosporanate for the benzhydryl7-(1,3-dithiolan-2-imino)cephalosporanate above, results in theformation of t-butyl 7-(1,3-dithiolan-2-imino)-4-methyl-Δ²-cephalosporanate, 2,2,2-trichloroethyl7-(1,3-dithiolan-2-imino)-4-methyl-Δ² -cephalosporanate, formyloxymethyl7-(1,3-dithiolan-2-imino)-4-methyl-Δ² -cephalosporanate andpivaloyloxymethyl 7-(1,3-dithiolan-2-imino)-4-methyl-Δ²-cephalosporanate, respectively.

EXAMPLE 2 Benzhydryl 7-(1,3-dithiolan-2-imino)-4-methyl-Δ²-desacetoxycephalosporanate

To a solution of 0.82 ml of diisopropylamine dissolved in 50 ml of drytetrahydrofuran (freshly distilled from lithium aluminum hydride) isadded 2.3 ml of butyl lithium with stirring at -50° C. under a blanketof argon. A solution of 2.4 g of benzhydryl7-(1,3-dithiolan-2-imino)desacetoxycephalosporanate dissolved in 20 mlof dry dimethylformamide is added via dropwise addition with stirring at-50° C. to this lithium diisopropylamide solution. The resulting lightyellow solution is stirred at -50° C. for 20 minutes and a solution of4.0 ml of methyl iodide dissolved in 10 ml of dimethylformamide israpidly added thereto. To reaction mixture is stirred at -50° C. for 15minutes and allowed to warm gradually to room temperature with continuedstirring. The reaction mixture is quenched in pH 4.5 phosphate bufferand the whole extracted with chloroform. The chloroform extracts arecombined, washed with water (three times), dried over anhydrousmagnesium sulfate, and evaporated to dryness in vacuo. The light yellowoil is dissolved in ethyl acetate, diluted with ether and the resultingsolution washed with water (three times), followed by a wash with asaturated solution of sodium chloride, and dried over anhydrousmagnesium sulfate. Removal of the solvents in vacuo leaves the desiredproduct, benzhydryl 7-(1,3-dithiolan-2-imino)-4-methyl-Δ²-desacetoxycephalosporanate as a solid yellow foam having a m.pt. of65°-70° C. (dec.).

Following essentially the same procedure, but substituting benzhydryl7-(1,3-dithiolan-2-imino)-3-[(5-methyl-1,3,4-thiadiazol-2-ylthio)methyl]decephalosporanate,benzhydryl7-(1,3-dithiolan-2-imino)-3-[(1-methyl-1,2,3-tetrazol-5-ylthio)methyl]decephalosporanateand benzhydryl7-(1,3-dithiolan-2-imino)-3-[(1,2,3-triazol-4-ylthio)methyl]decephalosporanatefor the benzhydryl 7-(1,3-dithiolan-2-imino)desacetoxycephalosporanateabove results in the formation of benzhydryl7-(1,3-dithiolan-2-imino)-4-methyl-Δ²-3-[(5-methyl-1,3,4-thiadiazol-2-ylthio)methyl]decephalosporanate,benzhydryl 7-(1,3-dithiolan-2-imino)-4-methyl-Δ²-3-[(1-methyl-1,2,3-tetrazol-5-ylthio)methyl]decephalosporanate, andbenzhydryl 7-(1,3-dithiolan-2-imino)-4-methyl-Δ²-3-[(1,2,3-triazol-4-ylthio)methyl]decephalosporanate, respectively.

EXAMPLE 3 Benzhydryl7-(1,3-dithiolan-2-imino)-4-t-butoxycarbonylmethyl-Δ²-desacetoxycephalosporanate

Butyl lithium, 0.23 ml, is added with stirring to 0.56 ml ofdiisopropylamine dissolved in 10 ml of dry tetrahydrofuran (freshlydistilled from lithium aluminum hydride) at -50° C. under an argonblanket. A solution of 0.24 g of the benzhydryl ester of7-(1,3-dithiolan-2-imino)desacetoxycephalosporanic acid is dissolved in5 ml of dry dimethylformamide and added at -50° C. to the lithiumdiisopropylamide solution with stirring. Following continuous stirringfor an additional 15 minutes, a solution of 0.12 ml of t-butylbromoacetate dissolved in 1 ml of dimethylformamide is added viadropwise addition with stirring. The reaction mixture is allowed to warmslowly to room temperature with continuous stirring and is quenched inpH 4.5 phosphate buffer. The entire mixture is extracted withchloroform, the chloroform extracts combined, washed three times withwater, dried over anhydrous magnesium sulfate, and evaporated to drynessin vacuo to a light orange oil. This oil is dissolved in a small amountof chloroform, applied to a previously prepared thin layerchromatography silica gel plate and a broad band collected having a Rfof 0.2-0.5. This band of material is dissolved in chloroform, filtered,and evaporated in vacuo to yield 0.22 g of benzhydryl7-(1,3-dithiolan-2-imino)-4-t-butoxycarbonylmethyl-Δ²-desacetoxycephalosporanate, as a solid yellow foam having the followingNMR characteristics:

NMR (CDCl₃) δ1.43 (s, 9H), 1.77 (s, 3H), 3.40-3.75 (m, 6H), 4.83 (d, 1H,J=5 Hz), 5.53 (d, 1H, J=5 Hz), 6.13 (br.s, 1H), 6.93 (s, 1H), 7.40 (s,10H).

Following essentially the same procedure, but substituting bromoaceticacid, chloromethyl mesylate, benzyl chloride and diethylcarbonate forthe t-butyl bromoacetate above, results in the formation of benzhydryl7-(1,3-dithiolan-2-imino)-4-carboxymethyl-Δ²-desacetoxycephalosporanate, benzhydryl7-(1,3-dithiolan-2-imino)-4-chloromethyl-Δ² -desacetoxycephalosporanate,benzhydryl 7-(1,3-dithiolan-2-imino)-4-benzyl-Δ²-desacetoxycephalosporanate, and benzhydryl7-(1,3-dithiolan-2-imino)-4-ethoxycarbonyl-Δ²-desacetoxycephalosporanate.

EXAMPLE 4 7-(1,3-Dithiolan-2-imino)-4-methyl-Δ²-desacetoxycephalosporanic acid

Benzhydryl 7-(1,3-dithiolan-2-imino)-4-methyl-Δ²-desacetoxycephalosporanate, 0.50 g, prepared in accordance with Example2, is dissolved in 5 ml of reagent anisole and cooled to 0° C.Trifluoroacetic acid, 25 ml, is cooled to 5° C., added to the anisolesolution and the reaction mixture is stirred for 30 minutes. Thereaction mixture is poured into 150 ml of chloroform and evaporated invacuo to near dryness. The residue is dissolved in diethyl ether andextracted with 50 ml portions of a 4% aqueous solution of sodiumbicarbonate until the aqueous extracts remain basic. The sodiumbicarbonate extracts are combined, 100 ml of chloroform added theretoand acidified to pH 2.5 with stirring. The aqueous solution is separatedand extracted twice again with fresh chloroform. form. The combinedchloroform extracts are combined, dried over anhydrous magnesium sulfateand evaporated to a dry white foam in vacuo. The foam is triturated withdiethyl ether, filtered and dried to yield7-(1,3-dithiolan-2-imino)-4-methyl-Δ² -desacetoxycephalosporanic acidhaving a m.pt. of 201°-3° C. (dec.).

Following essentially the same procedure, but substituting benzhydryl7-(1,3-dithiolan-2-imino)-4-methyl-3-[(5-methyl-1,3,4-thiadiazol-2-ylthio)methyl]-Δ²-decephalosporanate, benzhydryl7-(1,3-dithiolan-2-imino)-4-methyl-3-[(1-methyl-1,2,3-tetrazol-5-ylthio)methyl]-Δ²-decephalosporanate and benzhydryl7-(1,3-dithiolan-2-imino)-4-methyl-3-[(1,2,3-triazol-4-ylthio)methyl]-.DELTA.²-decephalosporanate for the benzhydryl7-(1,3-dithiolan-2-imino)-4-methyl-Δ² -desacetoxycephalosporanate aboveresults in the formation of7-(1,3-dithiolan-2-imino)-4-methyl-3-[(5-methyl-1,3,4-thiadiazol-2-ylthio)methyl]-Δ²-decephalosporanic acid,7-(1,3-dithiolan-2-imino)-4-methyl-3-](1-methyl-1,2,3-tetrazol-5-ylthio)methyl]-Δ²-decephalosporanic acid and 7-(1,3-dithiolan-2-imino)-4-methyl3-](1,2,3-triazol-4-ylthio)methyl]-Δ² -decephalosporanic acid,respectively.

EXAMPLE 5

The following example illustrates the in vitro activity of the compoundsdescribed herein.

Trypticase soy broth is inoculated from a slant culture of the testbacterium the day prior to testing. The inoculated broth is incubatedfor 24 hours at 37° C. and 0.05 ml of the inoculated and incubated brothis added to 25 ml of melted (45°-50° C.) trypticase soy agar. The seededagar is poured into a 100 mm square petri dish and allowed to solidify.

Approximately 1 to 3 mg of purified7-(1,3-dithiolan-2-imino)-4-methyl-Δ² -desacetoxycephalosporanic acid isplaced directly upon the agar and the agar plate is incubated overnight.The following day the agar plates are examined for clear zones ofbacterial growth inhibition and the diameter of each zone measured andrecorded. Using the test organism Salmonella schottmuelleri, a clearzone of bacterial inhibition measuring 2 mm in diameter is obtained,whereas with the test organism Pseudomonas aeruginosa, a clear zone ofbacterial inhibition measuring 5 mm in diameter is obtained.

We claim:
 1. A 7-(1,3-dithiolan-2-imino)-Δ² -cephalosporanic acidderivative having the formula ##STR9## wherein R₁ is selected from thegroup consisting of 5-methyl-1,3,4-thiadiazol-2-ylthio,1-methyl-1,2,3,4-tetrazol-5-ylthio and 1,2,3-triazol-4-ylthio;R₂ isselected from the group consisting of hydrogen, t-butyl,2,2,2-trichloroethyl, benzhydryl, formyloxymethyl and alkanoyloxymethylin which the alkanoyl group contains from 2 to 5 carbon atoms; R₃ isselected from the group consisting of alkyl having from 1 to 4 carbonatoms, carboxymethyl, alkoxycarbonyl and (alkoxycarbonyl)methyl whereinthe alkoxy group has from 1 to 4 carbon atoms, halomethyl, benzyl andsubstituted benzyl wherein the benzyl substituent is methoxy or halo;andthe pharmaceutically acceptable salts thereof.
 2. A compound accordingto claim 1 wherein R₃ is alkyl.
 3. A compound according to claim 1wherein R₃ is (alkoxycarbonyl)methyl.
 4. A process for the preparationof a compound of claim 1 which comprises reacting a7-(1,3-dithiolan-2-imino)cephalosporanic acid having the formula##STR10## with an alkylating or acylating agent having the formula R₃ Yin which R₁ is selected from the group consisting of5-methyl-1,3,4-thiadiazol-2-ylthio, 1-methyl-1,2,3,4-tetrazol-5-ylthioand 1,2,3-triazol-4-ylthio; R₂ is selected from the group consisting ofhydrogen, t-butyl, 2,2,2-trichloroethyl, benzhydryl, formyloxymethyl andalkanoyloxymethyl in which the alkanoyl group contains from 2 to 5carbon atoms; R₃ is selected from the group consisting of alkyl havingfrom 1 to 4 carbon atoms, carboxymethyl, alkoxycarbonyl and(alkoxycarbonyl)methyl wherein the alkoxy group has from 1 to 4 carbonatoms, halomethyl, benzyl and substituted benzyl wherein the benzylsubstituent is methoxy or halo; and Y is a leaving group selected fromthe group consisting of halogen, alkoxy, alkylthio, alkoxycarbonylthio,--OSO₂ Z and ##STR11## wherein Z is alkyl, alkoxy and tolyl and each ofthe alkyl or alkoxy groups have from 1 to 4 carbon atoms; reacting saidcephalosporanic acid and alkylating or acylating agent in an anhydrousorganic solvent at a temperature of from -78° to 30° C. for a period offrom 1 to 24 hours in the presence of a strong base; and recovering the7-(1,3-dithiolan-2-imino)-Δ² -cephalosporanic acid therefrom.